Is exponential gravity a viable description for the whole cosmological history?

Here we analysed a particular type of $F(R)$ gravity, the so-called exponential gravity which includes an exponential function of the Ricci scalar in the action. Such term represents a correction to the usual Hilbert-Einstein action. By using Supernovae Ia, Barionic Acoustic Oscillations, Cosmic Microwave Background and $H(z)$ data, the free parameters of the model are well constrained. The results show that such corrections to General Relativity become important at cosmological scales and at late-times, providing an alternative to the dark energy problem. In addition, the fits do not determine any significant difference statistically with respect to the $\Lambda$CDM model. Finally, such model is extended to include the inflationary epoch in the same gravitational Lagrangian. As shown in the paper, the additional terms can reproduce the inflationary epoch and satisfy the constraints from Planck data.Comment: 20 pages, 6 figures, analysis extended, version published in EPJ

Correlative Analysis of TOEFL IBT Scores of Listening Skill Versus Scores of Business English Speaking Skill Among Binus University Sophomores

Article found out whether BINUS university sophomore\u27s TOEFL iBT scores of Listening skill are correlated with those of speaking skill. The research project was expected to result in the best teaching technique of delivering conversational tasks at BINUS University by using alternative approaches of integrated, isolated, or mixed skills. The research project applied the descriptive approach of quantitative method, and thus depends on numerical data. The research project examined the set of data under two skills of the same class groups, which were to compare the listening scores with the speaking ones. Then, the degree of correlation of the two skills was tested so as to find its significance. Interpretation and explanation of data was made based on the statistical results by using correlation research analysis. Based on the statistical results, the listening scores significantly correlated with those of the speaking skill, and there is a moderately linear relationship between these paired scores

The results of the correlational analysis.

The results of the correlational analysis.</p

Relationship between the traction speed and force on coal rock and the number of broken bonds.

Relationship between the traction speed and force on coal rock and the number of broken bonds.</p

Statistical significance for possible group differences in the 13 linguistic variables.

Statistical significance for possible group differences in the 13 linguistic variables.</p

Descriptive statistics of error subtypes.

Descriptive statistics of error subtypes.</p

Arrangement of drum picks and cutting section model.

(a) drum pick arrangement. (b) cutting section model.</p

Distribution of error subtypes.

Distribution of error subtypes.</p

Particle contact model parameters.

A coal model containing gangue was established by discrete elements to study the forces occurring when a shearer cuts coal, and a rigid-flexible coupled shearer section model was established in RecurDyn; the drum cutting process was simulated through bidirectional coupling. The dynamic distribution of the force chain was obtained when cutter teeth cut the coal rock. During the cutting process, the coal rock failure is caused by normal and tangential forces, with the latter having a major role. The ratio of the average tangential force to normal force was 1.34~1.79. When the rock is in the middle of the coal seam, the force (including normal and tangential forces) on the rock is the highest. Moreover, the force on the rock-coal interface is greater than that on the coal-rock interface. The results show that the force on the coal decreases with the increases in rotation speed. In contrast, the number of broken bonds increases. Further, the number of broken bonds and the force of coal increased nonlinearly with traction speed. Finally, the increase of tooth mounting angle decreased the force on the coal rock and the number of broken bonds, followed by an increase. As such, this study provides a reference for further theoretical research on forces in coal cutting.</div

Bidirectional coupling simulation.

(a) discrete element simulation. (b) RecurDyn simulation.</p